In recent years, fuel cells have drawn attention as an eco-friendly clean energy source that has high power generation efficiency and produces little harmful gas.
A solid oxide fuel cell (hereinafter also referred to simply as an “SOFC”), which is a type of fuel cells, comprises a fuel cell unit and current collectors, in which the fuel cell unit comprises a solid oxide electrolyte layer, a gas-permeable air electrode (cathode) and a gas-permeable fuel electrode (anode).
The solid oxide electrolyte layer serves as a partition wall, and electric power is generated when fuel gas such as hydrogen and hydrocarbon is supplied to the fuel electrode and oxygen-containing gas such as air is supplied to the other electrode, i.e. the air electrode.
The current collectors contact the fuel cell unit to collect charges of the fuel cell unit. The current collectors also form a fuel gas channel or an air channel between the current collectors and the fuel cell unit.
The air electrode of the fuel cell unit is made of a metal oxide that has higher electric resistance than metals.
Accordingly, a longer travel distance of charges in the air electrode results in decreased power generation efficiency. To avoid this, a current collection assisting layer is provided between the air electrode and the current collector to form a conductive path so as to reduce the electric resistance.
JP 2008-243513A or Patent Document 1 discloses a fuel cell stack in which a metal porous body such as an expanded metal is disposed between a carbon bipolar plate defining a gas channel and a membrane-electrode assembly.